The sealing of ball valves (i.e. the leak integrity) is usually provided by applying a load on the ball, such required load being greater for higher pressure operations. The load is normally set by a mechanical biasing element, typically a coil spring. Since the force maintaining the ball in a fixed position is relatively high, such valves are subject to high friction and wear. Wear occurs when the ball is repeatedly turned while being pressed against the housing or packing of the valve, which results in scratches appearing on the ball, reducing the valve's lifetime.
Friction causes particles to be generated, which further increase problems associated with wear. Leaks are likely to appear, and eventually, the valve will have to be repaired or replaced. This problem may be found in most ball valves available. Referring to U.S. Pat. No. 4,867,414, there is shown a ball valve having retractable floating valve seats to facilitate inspection and maintenance of the valve. In such a valve, a mechanism to replace the worn parts is provided, but the problems associated with wear are still present.
Another problem arises from the fact that valves are usually tuned at ambient temperature, but are mostly used at different temperatures, from cryogenic temperatures to temperatures of around 350° C. The behavior of each part of the valve may therefore differ greatly depending on the temperature range at which it is operated. Consequently, a valve can work perfectly when tuned and operated at ambient temperature, but important leakage may occur when the valve is used in a system operated at a different temperature.
In light of the above, there is a need for an improved valve, or an improved system for reducing wear and friction on the ball of a ball valve during movement of the ball. There is also a need for a method of operating a valve that would help reduce friction between the ball and the stationary body assembly of the valve.